Coiled tubing is commonly used in the oilfield industry, and it is also becoming more common to employ continuous coiled rod instead of conventional sucker rod, for example for the purpose of driving downhole pump equipment, thereby avoiding the need to thread together discrete rod sections via threaded couplers at the ends thereof.
Injectors for coiled tubing or continuous rod typically employ a pair of endless chains driven in counter-rotating directions in a common upright plane, and carrying gripper dies or blocks on the chains that have outward facing gripping surfaces to clench the continuous rod between the faces of opposed gripper dies on the two chains as they descend downward on adjacent, facing-together, parallel sides of the two chain paths. A respective skate is found inside the area around which each chain is driven in order to lie along this descending side of the chain, and the skates are displaceable toward one another, typically by hydraulic cylinders connected between the skates on opposite sides of the chains closing therearound, thereby forcing the descending gripper blocks toward one anotherto firmly grip the coil tubing or continuous rod between them.
Prior art in the general area of injector heads and gripper dies for same includes U.S. Pat. Nos. 5,094,340, 5,553,668, 5,918,671, 6,425,441, 6,516,891, 6,609,566, 6,880,629, 6,892,810, 7,051,814, 7,857,042 and 8,132,617, and U.S. Patent Application Publication 2012/0222855.
U.S. Pat. No. 5,133,405 of Elliston discloses a different style of coiled tubing injector in which only a single endless chain is employed instead of gripping the continuous string between grippers of two endless chains that are forced together by hydraulically displaced skates. The single chain configuration provides the unit with an ‘open face’ design, by which the injector can laterally engage with or disengage from the continuous string from a position therebeside, rather than requiring vertical insertion and withdrawal of the continuous string into and from the injector. The design relies on a hinged construction by which two halves of each gripper open and close to receive, grip and release the continuous string.
It would be desirable to achieve an open-face injector head design that could accommodate lateral placement of the injector on a previously deployed string of continuous rod that already resides downhole without relying on an openable and closeable two-piece gripper design like that of Elliston.
In conventional dual-chain injectors that use skates to force together the gripping dies of the two chains at facing together sides of their closed-loop paths, the ability to laterally engage the injector with the continuous string is prevented by the presence of hydraulic cylinders laterally interconnecting the two skates with one another across the gap between the chains in which the continuous string is to be received.
U.S. Patent Application Publication 2013/0240198 discloses an alternative coiled tubing injector design in which the conventional set of hydraulic cylinders extending between the two skates is replaced with a separate bank of cylinders for each skate. The respective bank of cylinders for each skate acts against the outer side of the skate to push it toward the other skate and grip the continuous rod between the dies of the two chains closing respectively around the skates. However, the frame of Hassard's injector lacks an open face that would accommodate lateral placement and removal of the injector to and from the continuous string.
Applicant has developed a new continuous rod injector providing open-face lateral access, which has a unique combination of features not seen in the prior art, parts of which may also prove useful in continuous coiled tubing applications and even in closed-faced injector frame designs.